Replace is_publishable_class() with relispublishable column in pg_class

Hello hackers,

I would like to propose an improvement to the way PostgreSQL
determines if a relation is eligible for logical replication.
Currently, this check is performed dynamically via
is_publishable_class(), which relies on hard-coded OID checks and
relkind.  As noted in the existing comments atop
is_publishable_class[1], the long-term solution is to add a boolean
column to pg_class and depend on that instead of OID checks.

Motivation
========
1) The check is performed frequently in the logical decoding path
(e.g., in pgoutput_change and pgoutput_truncate). Moving this to a
cached catalog attribute in pg_class allows for a simple check.
2) As suggested by Amit Kpila [2], for the upcoming Conflict Log Table
feature, we need a clean way to exclude these internal conflict log
tables from publication. A catalog flag allows us to set this property
at relation creation rather than adding more special cases.

Proposed Changes
===============
The attached patch implements the following:
1) Catalog Update: Adds relispublishable (bool) to pg_class.
2) Creation Logic: Input parameter is added to
heap_create_with_catalog() so that caller can pass whether the
relation is publishable or not.
3) Update pgoutput and other relevant places to utilize the new
pg_class column directly.

[1]
The best
* long-term solution may be to add a "relispublishable" bool to pg_class,
* and depend on that instead of OID checks.
*/
static bool
is_publishable_class(Oid relid, Form_pg_class reltuple)
{
..
}

[2] https://www.postgresql.org/message-id/CAA4eK1K8Aqm%2BjP_EMPF8H_3UJSEExdwDCaphq6%3DunZZMdcmD0A%40mail.gmail.com

-- 
Regards,
Dilip Kumar
Google